Gas turbine engines have secondary air systems which provide cooling to various engine parts. It is desirable to minimize cooling air requirements to improve engine efficiency, and hence secondary air is typically metered, such as through metering holes in an engine casing or similar structure. A simpler arrangement is sometime to meter air through gaps between adjacent parts in the secondary air system. However, since components tend to be made from differing materials, depending on their particular design requirements, this results in differing thermal growths, which may be significant depending on the materials, location in the engine, etc. The differing thermal expansion/contraction characteristics of various engine components can negatively affect the ability to meter air accurately, however, and hence the designer must optimize the gap size to, for example, provide a desired flow for a threshold or target operating segment of the aircraft cycle (e.g. cruise, take-off, etc.), and sub-optimal performance for other segments. Accordingly, there is a need to provide an improved air metering arrangement for gas turbine engines.